Porous ceramics have been developed for use as filters for removal or separation of beer yeast, bacteria, pharmaceuticals and high purity gases. They are important due to their resistance to reactivity and corrosion, and their stability at high temperatures. Most filters in use have pores sizes of over 50 microns although an alumina membrane has been prepared having pore 0.05 microns in diameter and void ratio of up to 40 to 50%.
Of particular interest in this application is the ceramic material AlF.sub.3, which can be used in numerous catalytic hydrocarbon conversion processes. AlF.sub.3 prepared by most prior art methods and available commercially is a fine powder which cannot be extruded, pelletized or formed into a membrane. It is also characterized by very low surface areas, normally less than 5 m.sup.2 /gm. An AlF.sub.3 extrudate has been prepared having surface areas ranging from 10 to 50 m.sup.2 /gm, however this process requires the use of hazardous fluorocarbons and does not result in a product as pure as provided by this invention.
Therefore, it is necessary to develop ceramic materials with minimum pore size, maximum specific surface area, and maximum porosity that can operate in corrosive and oxidizing environments and to provide a safe process for making these materials.